The presence and growth of micro-organisms in aqueous systems, especially in industrial water systems, is a concern. Examples of industrial water systems where micro-organisms are a concern include cooling water systems, pulping and papermaking systems and oil and gas field water systems.
The presence of micro-organisms in industrial water systems may result in the formation of deposits on system surfaces. These deposits or slime can give rise to various problems. In cooling water systems, slime may restrict water flow, reduce heat transfer efficiency, cause corrosion and may be aesthetically unappealing especially if algae are present due to their visible green pigmentation. Corrosion can also occur in industrial water systems in the absence of visible slime through the action of micro-organisms.
In pulp and paper mill systems, slime formed by micro-organisms may cause fouling, plugging, or corrosion of the system. The slime may also break loose and become entrained in the paper produced causing blemishes, holes, tears, and odour in the finished product. The end result may therefore be unusable product and wasted output.
Slime can also be a problem in oil and gas field water systems and may cause energy losses due to increased fluid frictional resistance, formation plugging and corrosion. The slime may harbour a mixture of aerobic and anaerobic bacteria that are responsible for the production of hydrogen sulfide gas. The hydrogen sulfide may cause souring of oil and gas which may reduce the quality of these products and increase treatment costs.
Pseudomonas aeruginosa bacteria are commonly present in air, water and soil. These bacteria continually contaminate open cooling water systems, pulping and papermaking systems and oil and gas field water systems and are among the most common slime formers. Slime may be viewed as being a mass of cells stuck together by the cementing action of the gelatinous secretions around each cell. The slime entraps other debris, restricts water flow and heat transfer and may serve as a site for corrosion.
Chlorella vulgaris algae are also commonly present in air, water and soil. These algae continually contaminate open cooling water systems and their growth turns the water and surfaces in these systems green. They also provide a food source for bacteria, which can stimulate slime formation, and protozoa which can harbour the pathogenic bacterium Legionella pneumophila. 
A known method of controlling microbial growth in aqueous systems is to use biocides. While biocides are known to inhibit microbial growth the biocidal effect is generally of limited duration. The effectiveness of known biocides may be rapidly reduced as a result of exposure to negative influences. Negative influences may include temperature, pH or reaction with ingredients present in the system which neutralizes their biocidal effect. Therefore, the use of such biocides may involve continuous or frequent addition and their application at multiple sites or zones in the system to be treated. The cost of the biocide treatment and the labour costs associated with the application of known biocides may therefore be significant.
Known biocides are also highly toxic in the quantities known to be required for effective control of microbial populations. As a result, the amount of biocides that can be safely discharged into the environment may be limited by environmental regulations. Therefore, the need exists for improved methods for controlling microbial growth in aqueous systems.
As noted above, known biocides have a number of limitations including the large quantities of biocides which typically have to be used to achieve the desired biocidal effect and the potential harmful effects on the environment of biocides and therefore reducing the amount necessary for control and thus the quantity released to the environment has many benefits.
Accordingly, the present invention aims to address at least one disadvantage associated with the prior art whether discussed herein or otherwise.